There are two basic types of closures for small, hand-held, squeezable or rigid containers of products such as lotions, shampoos, fluent food products (e.g., ketchup, bottled water, etc.), viscous food products (e.g., peanut butter), powders, cleaning compositions, and the like.
One basic type of closure is a simple one-piece cap which can be screwed on and off or which is held on the container with a releasable snap-fit bead engagement.
The other basic type of closure is a “dispensing” closure, and one form of such a dispensing closure is a hinged dispensing closure which consists of (1) a body component designed to be sealingly applied to a container neck or finish, (2) a lid component, and (3) a hinge attaching the lid to the body so as to permit the lid to be moved between an open position and a closed position. The body component has a dispensing orifice or opening which permits product to be squirted, poured, spooned, or otherwise expelled, discharged, or dispensed from the container. The lid component contains a seal member which, when the lid is in the closed position, seals the body dispensing orifice to prevent unwanted discharge of product from the container.
Hinged dispensing closures (as well as many other articles of irregular or asymmetrical shapes which may have thin members interconnecting two or more masses) are made of rigid or semi-rigid thermoplastic resins such as polyethylene, polypropylene, and the like, and have been present in the commercial market for a number of years. Packages incorporating such dispensing closures are very advantageous in providing convenience and aesthetic appeal in the dispensing of products from containers. However, dispensing closures have historically suffered from a cost disadvantage compared to more simple non-dispensing closures owing to the complexity of molding dispensing closures.
Hinged dispensing closures are typically or conventionally injection molded either as a single, unitary structure having a body, lid, and hinge or as separate body and lid components which must be subsequently assembled to produce the final, assembled closure in which the body and lid are hinged together. When a dispensing closure is injection molded as a multiple piece assembly (e.g., body piece and lid piece), a separate mold is required for each of the component pieces. Even if the dispensing closure is instead injection molded as a single, unitary component, the amount of surface area or space occupied by the unitary component in the mold is approximately twice that of a comparable mold for a simple non-dispensing closure. Thus, the injection molding process for such a dispensing closure typically requires approximately twice the investment in injection molds, injection molding presses, and other molding resource costs compared to the process for injection molding a simple non-dispensing closure for the same container finish. It would, therefore, be of significant commercial advantage to a manufacturer to have an improved method by which the manufacturer could produce, at a very high output rate and with little or no waste, hinged dispensing closures for capital investment costs and operating costs comparable to costs for producing to non-dispensing closures.
The method of injection molding has long been used to produce thermoplastic resin articles, and the method has been made more efficient over time by the introduction of improved electronic controls, hydraulic systems, etc. It has also been possible to increase the productive output of the process by the introduction of larger mold structures with an increased number of cavities (i.e., “cavitation”). In addition, molds with multiple molding surfaces (e.g., “stacked molds”) are now in commercial use. Each of these improvements has helped to increase the productive output of a single molding machine, but not without size, weight, and investment cost penalties. The cost, size, and weight of the larger machines and molds increase disproportionately more with the increase in size, cavitation, and complexity of the molds and machines, while the rate of parts produced increases only in generally direct proportion to the increased number of mold cavities. In this regard, it can be seen that increases in the size and weight of larger injection molding machines could approach a practical limiting case of productive return for the required financial and resource investment.
Another method of molding plastic articles, the “compression” molding method, has existed for many years. In the earliest practice, compression molding was used to make rigid thermosetting resin plastic articles from resins such as phenol formaldehyde, urea formaldehyde, and the like. More recently, compression molding processes make semi-rigid plastic articles from thermoplastic resin such as polyethylene, polypropylene, and the like.
In the case of making thermosetting resin plastic articles by the compression molding method, the uncured resin, usually in granular or powder form, is charged into a heated mold cavity of a mold cavity segment, and the mold is closed by bringing a mold core segment against the cavity segment with great force to create high pressure in the cavity. The resultant combination of heat and pressure causes the resin material first to melt into a semi-solid state to completely fill the mold volume between the core segment and cavity segment, and subsequently to become rigid through reactive chemical cross linking of the resin. After a sufficient curing time, the molded article is removed from the mold and allowed to cool to ambient temperature before further handling or finishing.
Plastic articles made by the thermosetting resin compression molding method are typically very durable and relatively heavy owing to the physical properties of the resin. Owing to the flow limitations of the resin during the molding step, such molded articles are also typically limited in their final geometric proportions, tending to be of symmetrically shaped cylindrical, spherical, or rectangular solid configurations. In practice, the resin cannot successfully be made to flow into a highly irregular geometrical form.
In the case of making thermoplastic resin plastic articles by conventional compression molding, a precisely measured cylindrical charge of the heated, molten, thermoplastic resin is created by operation of an extruder, metering pump, and cutting knife, and the cylindrically shaped charge is dropped into a cooled cavity of a mold. The mold is then closed by forcing a mold core segment against the mold cavity segment. Upon closing the mold segments, the pressurized molten plastic resin quickly fills the volume between the core and cavity. After a brief cooling period, the mold is opened, and the finished molded article is removed from the mold, ready for immediate use. This method and products produced by it are already well-known in commerce and are described in various patents such as U.S. Pat. Nos. 4,343,754; 4,664,280; 4,674,643; 4,497,765; 5,650,113; and 5,658,518, and WO 01/34362 A1 (PCT/GB00/04175).
Compared to a commercial injection molding operation, the cycle time needed between introduction of the molten plastic into a commercial compression molding machine and removal of the finished article is shorter. Heretofore, however, much like their compression molded thermosetting counterparts, compression molded thermoplastic articles, while accommodating faster production at lower overall cost compared to their injection molded counterparts, have been limited to symmetrically shaped, principally cylindrical, configurations owing to the flow limitations of the molten thermoplastic resin as the mold segments are moved into the closed position to shape the resin into the desired article form. Because of such geometric and flow constraints, it has not been possible heretofore to cost effectively use a compression molding process to produce articles of unusual shapes, such as hinged dispensing closures, on a commercial scale.
As currently practiced in conventional commercial applications, compression molding of a thermoplastic resin article relies upon physically dropping a cylindrical shaped, measured charge or pellet of molten resin in a relatively random position in the mold cavity. In the case of a hinged dispensing closure which has a body part and a lid part of unequal physical weights and volumes, and which two parts are joined by a thin film hinge, the inventors have discovered that it is not acceptable to rely on the random placement of a symmetrical, cylindrically shaped resin charge or pellet within the mold cavity. When the mold is closed to compress such a pellet, it is not possible to reliably and consistently cause the molten plastic resin to flow into all regions of the void volume between the mold core and cavity before solidification takes place.